package basic.basic_class03;

/**
 * 反转单向和双向链表
 * 【题目】 分别实现反转单向链表和反转双向链表的函数。
 * 【要求】 如果链表长度为N，时间复杂度要求为O(N)，额外空间
 * 复杂度要求为O(1)
 */
public class Code_07_ReverseList {
    // 单项链表节点
    public static class Node {
        public int value;
        public Node next;

        public Node(int data) {
            this.value = data;
        }
    }

    // 双向链表节点
    public static class DoubleNode {
        public int value;
        public DoubleNode last;
        public DoubleNode next;

        public DoubleNode(int data) {
            this.value = data;
        }
    }

    // 递归反转单链表
    public static Node reverseList(Node head) {
        if(head == null || head.next == null) return head;
        Node last = head.next;
        Node next = reverseList(head.next);
        last.next = head;
        head.next = null;
        return next;
    }

    // 非递归反转单链表
    public static Node reverseList2(Node head) {
        if(head == null || head.next == null) return head;
        Node pre = null;
        Node next = null;
        while(head != null){
            next = head.next;
            head.next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }

    /**
     * 反转双向环形链表
     * @param head
     * @return
     */
    public static DoubleNode reverseList(DoubleNode head) {
        if(head == null || head.next == null) return head;
        DoubleNode pre = null;
        DoubleNode next = null;
        while(head != null) {
            next = head.next;
            head.next = pre;
            head.last = next;
            pre = head;
            head = next;
        }
        return pre;
    }

    public static void printLinkedList(Node head) {
        System.out.print("Linked List: ");
        while (head != null) {
            System.out.print(head.value + " ");
            head = head.next;
        }
        System.out.println();
    }

    public static void printDoubleLinkedList(DoubleNode head) {
        System.out.print("Double Linked List: ");
        DoubleNode end = null;
        while (head != null) {
            System.out.print(head.value + " ");
            end = head;
            head = head.next;
        }
        System.out.print("| ");
        while (end != null) {
            System.out.print(end.value + " ");
            end = end.last;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Node head1 = new Node(1);
        head1.next = new Node(2);
        head1.next.next = new Node(3);
        printLinkedList(head1);
        head1 = reverseList(head1);
        printLinkedList(head1);

//        DoubleNode head2 = new DoubleNode(1);
//        head2.next = new DoubleNode(2);
//        head2.next.last = head2;
//        head2.next.next = new DoubleNode(3);
//        head2.next.next.last = head2.next;
//        head2.next.next.next = new DoubleNode(4);
//        head2.next.next.next.last = head2.next.next;
//        printDoubleLinkedList(head2);
//        printDoubleLinkedList(reverseList(head2));
    }
}
